Reloading a page in Chrome from Aquamacs

2011-09-01

The Emacs function browse-url tells your browser to open a URL. It's pretty simple. Your default browser will open the URL in a new tab or window.

If we're editing a web page, we'll probably be reloading it pretty often in the browser. I couldn't find a way to make Emacs tell our browser to reload a URL if the browser already has that URL open in some tab. So let's write some elisp.

This code is Mac-specific, because it relies on AppleScript to talk to the browser. It works (for me) in both Aquamacs and Emacs.app.

This code is also Chrome-specific, because Safari has a slightly different AppleScript dictionary and Firefox isn't scriptable.

So anyway, our goal is to have the visible tab of Chrome's front window show our URL. If Chrome already has a tab in any of its windows showing the URL, it should make that tab visible, bring that window to the front, and reload that tab. If there's no such tab, it should make one in the frontmost window. And if Chrome doesn't have any windows open, it should make a new window.

So we need an elisp function that takes a URL and does all of that, using AppleScript. Here it is:

(defun mayoff:open-url-in-chrome (url)
  "Open URL in Google Chrome.  I use AppleScript to do several things:
  1. I tell Chrome to come to the front. If Chrome wasn't launched, this will also launch it.
  2. If Chrome has no windows open, I tell it to create one.
  3. If Chrome has a tab showing URL, I tell it to reload the tab, make that tab the active tab in its window, and bring its window to the front.
  4. If Chrome has no tab showing URL, I tell Chrome to make a new tab (in the front window) showing URL."
  (when (symbolp url)
    ; User passed a symbol instead of a string.  Use the symbol name.
    (setq url (symbol-name url)))
  (do-applescript (format "
tell application \"Google Chrome\"
        activate
        set theUrl to %S

        if (count every window) = 0 then
                make new window
        end if

        set found to false
        set theTabIndex to -1
        repeat with theWindow in every window
                set theTabIndex to 0
                repeat with theTab in every tab of theWindow
                        set theTabIndex to theTabIndex + 1
                        if theTab's URL = theUrl then
                                set found to true
                                exit
                        end if
                end repeat

                if found then
                        exit repeat
                end if
        end repeat

        if found then
                tell theTab to reload
                set theWindow's active tab index to theTabIndex
                set index of theWindow to 1
        else
                tell window 1 to make new tab with properties {URL:theUrl}
        end if
end tell
  " url)))

Now we can evaluate an expression like

(mayoff:open-url-in-chrome "http://qwan.org/2011/09/01/reloading-a-page-in-google-chrome-from-emacs-on-a-mac/")

to view that URL in Chrome, reloading it if it's already loaded.

Of course, we're not going to want to type all that out every time we update the page. What we really want is a way to set a URL to be loaded, and then a way to run mayoff:open-url-in-chrome on that URL. I like to put both actions on F5, using C-u F5 to set the URL and plain F5 to send it to the browser. Here's the code:

(defvar mayoff:open-in-chrome-url nil
  *The URL that the mayoff:open-in-chrome function will send to Google Chrome.")

(defun mayoff:open-in-chrome (arg)
  "Open or reload a file in Google Chrome.  If you give me a prefix argument, I get Chrome's currently-displayed URL and save it for the future.  If you don't give me a prefix argument, I send the previously-saved URL to Chrome for reloading."
  (interactive "P")
  (cond
   (arg (setq mayoff:open-in-chrome-url (do-applescript "tell application \"Google Chrome\" to get window 1's active tab's URL")))
   ((not mayoff:open-in-chrome-url) (error "You haven't set a URL for me to send to the browser."))
   (t (save-buffer)
      (mayoff:open-url-in-chrome mayoff:open-in-chrome-url))))

(global-set-key (kbd "<f5>") 'mayoff:open-in-chrome)

Mission accomplished.